Process for the preparation of lithium metaphosphate

ABSTRACT

The present invention provides a process for the preparation of lithium metaphosphate comprising reacting a lithium source and a phosphorous source in solid state to obtain lithium metaphosphate.

FIELD OF THE INVENTION

The present invention relates to a novel process for the preparation of lithium metaphosphate (LiPO₃) by a solid state thermal reaction. This compound is useful as an intermediate for the preparation of lithium hexa fluorophosphates (LiPF₆). This salt is a good electrolyte in aqueous, non-aqueous, solid and selected polymer medium. The present invention particularly relates to the preparation of lithium metaphosphate (LiPO₃) compound which is the basic chemical for the preparation of lithium hexafluorophosphates (LiPF₆) by a novel solid state method which is not hitherto attempted anywhere.

BACKGROUND OF THE INVENTION

Prior art literature on lithium metaphosphate (LiPO₃) discloses the reaction of lithium salts with metaphosphoric acid, which is obtained by heating pyro-phosphoric acid or ortho-phosphoric acid. The reaction occurring for the above two thermal processes are as follows:

1. H₄P₂O₇ → 2HPO₃ + H₂O 2. H₃PO₃ → HPO₃ + H₂O HPO₃ + LiOH → LiPO₃ + H₂O

REFERENCE

Advanced Inorganic Chemistry, S. Sathiya Prakash G. D. Tuli, S. K. Basu and R. D. Radan, S. Chand & Co., New Delhi, p. 988 (1998).

The above methods need controlled conditions for the preparation of lithium metaphosphate. The above methods for the preparation of lithium metaphosphate also suffer from the following disadvantages:

1. More than one step is involved to prepare LiPO₃.

2. Needs crystallization procedure once the product is formed from aqueous solution.

OBJECTS OF THE INVENTION

The main object of this present invention is to provide a simple novel process for the synthesis of lithium meta phosphate (LiPO₃) which obviates the draw back mentioned above.

Another object of the present invention is to provide a complete solid state reaction procedure for the preparation of LiPO₃.

Another object of the invention is to provide a single step process to obtain LiPO₃.

Yet another object of the invention is to get high yield of the product LiPO₃ (>90%).

SUMMARY OF THE INVENTION

The above and other objects have been achieved by the solid state method for the preparation of lithium metaphosphate of the invention.

Accordingly, the present invention provides a process for the preparation of lithium metaphosphate comprising reacting a lithium source and a phosphorous source in a ratio of 1:1-2 in solid state at a temperature in the range of 300 to 650° C. to obtain the desired lithium metaphosphate.

In one embodiment of the invention, the lithium source is selected from the group consisting of Li₂O, LiCO₃, LiOH, LiNO₃ and any mixture thereof.

In another embodiment of the invention, the phosphorous source is selected from the group consisting of ammonium pyrophosphate, ammonium orthophosphate, diammonium hydrogen phosphate and ammonium dihydrogen phosphate and any mixture thereof.

In another embodiment of the invention, the reaction is carried out in solid state in a single step.

In yet another embodiment of the invention, the reaction is carried out at a temperature of 350° C. for a time period of 12 hours and the lithium source is selected from Li₂O, LiOH and LiNO₃.

In another embodiment of the invention, the reactive materials are heated in a muffle or in an electric furnace.

In yet another embodiment of the invention, Li₂CO₃ is reacted with the phosphorous source at a temperature of 600° C.

In another embodiment the lithium source and the phosphorous source are mixed and ground well before being heated.

In another embodiment of the invention, the lithium source and the phosphorous source are mixed in an equimolar ratio.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The FIGURE shows the X-ray analysis of the product obtained by the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferably equimolar quantities of ammonium pyrophosphate/ammonium orthophosphate/ diammonium hydrogen phosphate/ammonium dihydrogen phosphate is allowed to react with Li₂O/LiCO_(3/)LiOH/LiNO₃ at a temperature of 350° C. in a muffle furnace for a period of 12 hours to get lithium meta phosphate (LiPO₃) which was confirmed by X-ray analysis. The reaction occurring with lithium salts and ammonium salts of pyro and ortho phosphates are as follows:

1. (NH₄)₄P₂O₇ + 2LiOH → 2LiPO₃ + 4NH₃ + 3H₂O 2. (NH₄)₃PO₄ + LiOH → LiPO₃ + 3NH₃ + 2H₂O 3. (NH₄)₂HPO₄ + LiOH → LiPO₃ + 2NH₃ + 2H₂O 4. (NH₄)H₂PO₄ + LiOH → LiPO₃ + NH₃ + 2H₂O

A novel method for the preparation of LiPO₃ is developed wherein equimolar quantities of LiOH/Li₂CO_(3/)Li₂O/LiNO₃. This mixture is ground well and then transferred into a porcelain/silica crucible. In the mixture, the lithium salt content to the phosphorous content should be in the molar ratio of 1:1. The silica crucible containing the mixture is introduced into an electric furnace. The furnace was slowly heated to 350° C. and the heating was continued for 12 hours keeping the same temperature. When the reaction is over, the furnace was cooled and the product was ground well and then examined for its purity and identity.

In the process of the invention for the synthesis of lithium meta phosphate lithium salt (LiOH/Li₂CO_(3/)Li₂O/LiNO₃) is mixed with equimolar quantities of ammonium pyrophosphate or ammonium orthophosphae or diammonium hydrogen phosphate or ammonium dihydrogen phosphate and the mixture is ground well and then transferred the mixture into a silica crucible and then the crucible containing the mixture is heated to 350° C. continuously in an electric furnace to get LiPO₃. The reactants are solid state materials and are heated in a muffle or in an electric furnace. Pure dry AR Li₂O or Li₂CO₃ or LiOH or LiNO₃ was mixed with any one of the salts of ammonium pyrophosphate or ammonium orthophosphate or diammonium hydrogen phosphate or ammonium dihydrogen phosphate in equilmolar quantities. The Li and P content of the salt was kept in the ratio 1:1. The mixture of the lithium and the phosphate salts are ground well and then the grounded mixture was transferred into silica vessel. The vessel was then introduced into a electric furnace. The furnace was slowly heated to 350° C. continuously for 12 hours and then the resultant product was powdered well and then analyzed for its purity and identity.

The following examples are given by way illustration and therefore should not be construed to limit the scope of the prevent invention.

EXAMPLE 1

A mixture of dry AR Li₂CO₃ and dry AR (NH₄) ₄P₂O₇ was taken in 1:2 molar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 600° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition Li₂CO₃ 0.74 g (NH₄)₄P₂O₇ 4.72 g Initial Temperature 100° C. Time 1 hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 2

A mixture of dry AR Li₂CO₃ and dry AR (NH₄) ₃PO₄ was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 600° C. for 12 hours continuously. The resultant product is LiPO₃. Particle size of the mixture 5-10 mμ.

Components Composition Li₂CO₃ 0.74 g (NH₄)₃PO₄ 1.67 g Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 3

A mixture of dry AR Li₂CO₃ and dry AR (NH₄) ₂HPO₄ was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 600° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition Li₂CO₃ 0.74 g (NH₄)₂HPO₄ 1.15 g Initial Temperature 100° C. Time 1 Hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >91% Particle size of the mixture 5-10 mμ.

EXAMPLE 4

A mixture of dry AR Li₂CO₃ and dry AR (NH₄)HPO₄ was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was heated initially slowly and finally to 600° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition Li₂CO₃ 0.74 g (NH₄)HPO₄ 1.32 g Initial Temperature 100° C. Final Temperature 600° C. Time 12 hours. Nature of the product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 5

A mixture of dry AR LiOH and dry AR (NH₄)₄P₂O₇ was taken in 1:2 molar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition LiOH 0.74 g (NH₄)₄P₂O₇ 4.72 g Initial Temperature 100° C. Time 1 Hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 6

A mixture of dry AR LiOH and dry AR (NH₄) ₃PO₄ was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition LiOH 0.74 g (NH₄)₂HPO₄ 1.15 g Temperature 350° C. Time 12 hours Nature of the product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 7

A mixture of dry AR LiOH and dry AR (NH₄) ₂HPO₄ was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition LiOH 0.24 g (NH₄)₂HPO₄ 1.32 g Initial Temperature 100° C. Time 1 hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 8

A mixture of dry AR LiOH and dry AR (NH₄)₄P₂O₇ was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was heated initially slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition LiOH 0.24 g (NH₄)₄P₂O₇ 4.92 g Initial Temperature 100° C. Time 1 hour Final temperature 600° C. Time 12 hours Nature of product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 9

A mixture of dry AR LiNO₃ and dry AR (NH₄)₄P₂O₇ was taken in 1:2 molar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition LiNO₃ 0.69 g (NH₄)₄P₂O₇ 4.92 g Initial Temperature 100° C. Time 1 hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >91% Particle size of the mixture 5-10 mμ.

EXAMPLE 10

A mixture of dry AR LiNO₃ and dry AR (NH₄) ₂HPO₄ was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition LiNO₃ 0.69 g (NH₄)₂HPO₄ 1.32 g Initial Temperature 100° C. Time 1 hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 11

A mixture of dry AR LiNO₃ and dry AR (NH₄)HPO₄ was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was heated initially slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition LiNO₃ 0.69 g (NH₄)HPO₄ 1.15 g Initial Temperature 100° C. Time 1 hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 12

A mixture of dry AR Li₂O and dry AR (NH₄)₄P₂O₇ was taken 1:2 molar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition Li₂O 0.30 g (NH₄)₂P₂O₇ 4.92 g Initial Temperature 100° C. Time 1 hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >91% Particle size of the mixture 5-10 mμ.

EXAMPLE 13

A mixture of dry AR Li₂O and dry AR (NH₄)₂HPO₄ was taken in equimolar ratio. The mixture was ground well as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was initially heated slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition Li₂O 0.30 g (NH₄)₂HPO₄ 1.32 g Initial Temperature 100° C. Time 1 hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >90% Particle size of the mixture 5-10 mμ.

EXAMPLE 14

A mixture of dry AR Li₂O and dry AR (NH₄)HPO₄ was taken in equimolar ratio. The mixture was ground well so as to get particle size in the range of 5-10 μm. The above mixture was taken in a silica/porcelain crucible and was then introduced in a muffle/electric furnace. The mixture was heated initially slowly and finally to 350° C. for 12 hours continuously. The resultant product is LiPO₃.

Components Composition Li₂O 0.30 g (NH₄)HPO₄ 1.15 g Initial Temperature 100° C. Time 1 Hour Final Temperature 600° C. Time 12 hours Nature of the product Transparent Efficiency of the process >91% Particle size of the mixture 5-10 mμ.

CONCLUSIONS

Ammonium pyrophosphate or ammonium orthophosphate or diammonium hydrogen phosphate or ammonium dihydrogen phosphate reacts with Li salts like LiOH/Li₂O/Li₂CO₃/LiNO₃ such that Li salt and P salt mixture combinations are in equimolar proportion (1:1) to form LiPO₃, when the temperature of heating is maintained at about 350° C. for 12 hrs continuously. In the absence of Li₂CO₃ in any of the above reaction mixture with ammonium pyrophosphate or ammonium orthophosphate or diammonium hydrogen phosphate or ammonium dihydrogen phosphate the temperature is 350° C. The colour of the product is white and the particle size can be brought to any decided level. X-ray analysis confirms the LiPO₃ formation.

The main advantages of the present invention are:

1. It is a single step, thermal procedure for the preparation of LiPO₃

2. It is a solid state thermal procedure.

3. Any of the lithium salts like LiOH/Li₂CO₃/Li₂O/LiNO₃ is mixed with ammonium pyrophosphate or ammonium orthophosphate or diammonium hydrogen phosphate or ammonium dihydrogen phosphate to give LiPO₃.

4. This is a base material for the preparation of LiPF₆. 

We claim:
 1. A process for the preparation of lithium metaphosphate comprising reacting a lithium source and a phosphorous source in a ratio of 1:1-2 in solid state at a temperature in the range of 300 to 650° C. to obtain the desired lithium metaphosphate.
 2. A process as claimed in claim 1 wherein the lithium source is selected from the group consisting of Li₂O, LiCO₃, LiOH, LiNO₃ and any mixture thereof.
 3. A process as claimed in claim 1 wherein the phosphorous source is selected from the group consisting of ammonium pyrophosphate, ammonium orthophosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate and any mixture thereof.
 4. A process as claimed in claim 1 wherein the reaction is carried out in solid state in a single step.
 5. A process as claimed in claim 1 wherein the reaction is carried out at a temperature of 350° C. for a time period of 12 hours and the lithium source is selected from the group consisting of Li₂O, LiOH and LiNO₃.
 6. A process as claimed in claim 1 wherein the reactive materials are heated in a muffle or in an electric furnace.
 7. A process as claimed in claim 1 wherein Li₂CO₃ is reacted with the phosphorous source at a temperature of 600° C.
 8. A process as claimed in claim 1 wherein the lithium source and the phosphorous source are mixed and ground well before being heated.
 9. A process as claimed in claim 1 wherein the lithium source and the phosphorous source are mixed in an equimolar ratio. 